Tobacco product carrying catalytically active material and its use in a smokers&#39; article

ABSTRACT

The tobacco product carries on its surface catalytically active material for improving the burning process. The catalytically active material is selected from the group of crystalline and non-crystalline oxides and hydroxides of aluminium, e.g. gibbsite, having a particle size of 1 to 100 μm and a specific surface of 75 to 250 m 2 /g. With the use of the catalyst in the tobacco, the amount of noxious compounds in the mainstream and sidestream smoke can be considerably reduced in the combustion process of the smokers&#39; article during its consumption.  
     The said tobacco product is useful for smoker&#39;s articles comprising a filter, a tobacco rod and a wrapper. In such articles the tobacco rod consists of the tobacco product.

[0001] This invention relates to a tobacco product carryingcatalytically active material, to articles for smoking containing such atobacco product and more particularly to cigarettes which containnon-zeolitic catalysts in the tobacco rod. The catalytically activematerial is useful for reducing toxic components in tobacco smoke ofsmokers' articles, particularly of cigarettes.

[0002] As is well known, two kinds of smoke arise during the smoking ofa cigarette, the mainstream smoke and the sidestream smoke. Themainstream smoke is the smoke which enters the mouth of the smoker whenhe draws on the cigarette through the filter part, while the sidestreamsmoke is the smoke which is released by the smouldering combustion ofthe cigarette in the interim phases. From technical literature it can belearned that approximately twice as much tobacco is burned during theglowing of a cigarette between the puffs than during the puffs.

[0003] Although in the prior art many—albeit unsatisfactory—means ofreducing the mainstream smoke of noxious substances have been proposed,there has been no solution so far which makes it possible to remove thenoxious substances from the sidestream smoke in sufficient manner.

[0004] Large pore zeolites were the first catalysts to be found toreduce significant amounts of undesirable compounds in sidestream aswell as mainstream smoke (U.S. Pat. No. 5,727,537, EP-A-0 740 907).However, zeolites have an inherent disadvantage in that larger PAHmolecules like benzo(a)pyrine, one of the worst carcinogenic smokeconstituents, are not reduced in the mainstream. The overall PAHreduction values are less than a 25% in the mainstream compared to over50% in the sidestream. The disappointing performance in the mainstreamhas been assigned to the sieving effect of the pore openings in thezeolite framework structure (W. M. Meier and K. Siegmann, Microporousand Mesoporous Materials, 33 (1999) 307-310).

[0005] U.S. Pat. Nos. 3,572,348 and 3,703,901 suggest the use ofzeolites for incorporating in tobacco material for reducing toxiccompounds in the smoke. However, the proposed zeolite compounds containsubstantial amounts of zinc besides palladium or platinum which are notsuitable for several reasons for a product which cannot be recycled.These typical preparations known in petrochemistry of those days wereheated in nitrogen (rather than burned in the presence of oxygen) andhave little to do with a burning cigarette, and the process waspyrolysis rather than combustion. Mainstream and sidestream could not bedistinguished in the set-up used. Moreover, the use of zinc is notpermissible in open systems by environmental laws.

[0006] Described in EP-A-0 740 907 are smokers' articles wherein thetobacco comprises a catalyst of a zeolite compound. It is proposed thatthe catalyst in the tobacco be bound to the tobacco with or without abinding agent, such as silica gel or attapulgite, a meerschaum-like claymineral. Attempts to fix catalyst particles on the tobacco byelectrostatic deposition failed. The catalyst particles were observed todischarge on the tobacco fibers within seconds and sputtered. It wasfound that the use of binding agents has serious drawbacks because thecatalytic activity of the material which is bound by the agent isaffected. Without binding agent, the binding strength of thecatalytically active material to the tobacco is not sufficient, andtherefore a separation of the catalyst from the material can occureasily during the manufacturing process of smokers' articles or duringtransportation.

[0007] Zeolitic materials, both natural and synthetic, in appropriateform, can have catalytic capabilities for various kinds of organicreactions. Zeolites are microporous crystalline aluminosilicates whichhave definite crystal structures having a large number of cavitiesconnected to each other by channels. These cavities and channels areabsolutely uniform in size, and their dimensions can be determined byprobe molecules as well as by crystal structure analysis. In most casesthese data are known and do not have to be determined further. Since thedimensions of these pores are such that they sorb molecules ofparticular dimensions while rejecting those of larger dimensions, thesematerials have come to be known as “molecular sieves” and are utilizedin a variety of ways to take advantage of these properties.

[0008] Such molecular sieves comprise a large variety of structuraltypes (nearly 100; cf. D. H. Olson, W. M. Meier and Ch. Baerlocher,Atlas of Zeolite Framework Types, 5rd Edition, 2001, Elsevier,(formerly: Atlas of Zeolite Structure Types)) of crystallinealuminosilicates and isostructural materials with free pore diameters inthe range of 0.3 to 1.3 nm or 3 to 13 Å. These aluminosilicates can bedescribed as a rigid three-dimensional network of SiO₄ and AlO₄, whereinthe tetrahedra are cross-linked by sharing of oxygen atoms, the ratio ofall aluminium and silicon atoms to oxygen being 1:2. Such a networkcontaining aluminium is negatively charged, and requires for chargebalance one monovalent cation (e.g. Na or K) or half a divalent cation(e.g. Ca) for each Al in the network. These cations can be exchangedeither completely or partially using standard ion exchange techniques.Cation exchange is a possible means of fine tuning the critical porediameter in a particular application.

[0009] The pore volume of a typical zeolite is occupied by watermolecules before dehydration. Dehydrated or activated zeolites areexcellent sorbents for molecules which are small enough to pass throughthe apertures of the sieve. Syntheses using organic cations (such astetrapropylammonium) have led to “high silica zeolites”, which containonly few Al in the network, if any at all, and the compositionapproaches that of SiO₂. High silica zeolites are not unanimouslyconsidered to be zeolites; although they have the same kind ofstructure, their exchange capacities are comparatively low, theirselectivities very different, and these materials are hydrophobic.Consequently they are referred to as zeolite-like molecular sieves inthis specification, following widespread usage.

[0010] The sieving effect of the molecular sieve is based on the poresize. Sorption is also controlled by electrostatic interactions. Many ofthe chemical and physical properties are dependent upon the Al contentof the zeolite. A rising Si/Al ratio means an increased temperaturestability, up to 1000° C. in the case of silicalite, which is amolecular sieve with a pure SiO₂ framework structure. The selectivity ofthe inner surfaces changes from strongly polar and hydrophilic in thecase of the molecular sieves rich in aluminium to a polar andhydrophobic in the case of a zeolite with a modulus >400.

[0011] It has been discovered that the object of the present inventioncan be achieved by incorporating certain catalytically active materials,which fulfill the necessary catalytic criteria, into tobacco bydistributing the catalytically active material regularly on conditionedtobacco and by pressing the catalytically active material on thetobacco. When incorporated into the tobacco rod of a cigarette, thecatalytic properties of the material which is pressed on the tobacco candevelop its catalytic activity completely. The advantage is that thepores of the material remain open. Moreover the method assures an evendistribution of catalyst particles on the tobacco which isall-important.

[0012] Consequently there is a demand for smokers' articles, especiallyfilter cigarettes, whose mainstream as well as sidestream smoke issignificantly lower in noxious substances than with smokers' articles ofprior art.

[0013] A first object of the present invention is therefore to provide atobacco product having a considerably lower content of noxious compoundssuch as PAHs and nitrosamines in its smoke than known products and whichis free of the above-mentioned drawbacks.

[0014] To overcome the shortcomings of large pore zeolites like NaY inthe mainstream other catalyst materials have been investigated. Goodresults were obtained with oxides and hydroxides of aluminium. Thesematerials should have a particle size of around 1 μm (not smaller and bedusty) and a surface of some 100 m²/g or more.

[0015] In a first aspect, one subject matter of the present invention isthus a tobacco product carrying on its surface catalytically activematerial for improving the burning process, wherein the catalyticallyactive material is selected from the group of crystalline andnon-crystalline oxides and hydroxides of aluminium

[0016] In a second aspect, a further subject matter of the presentinvention is a smokers' article comprising a filter, a tobacco rod and awrapper in which the tobacco rod contains a catalyst selected from thegroup of oxides or hydroxides of aluminium. They are preferably acid orslightly acidic. The catalyst may contain Fe or Si in minor amounts(e.g. 0 to 3%) or more Si for amorphous material. The catalyst cancomprise particles consisting of single crystals or particles consistingof agglomerates of smaller crystals which are bound with a binder askaolinite (“granulate”). Normally the catalyst is not highlycrystalline. Typically the catalyst is selected from the compounds ofthe group alumina (Al-oxide), diaspore, natural or synthetic boehmite,natural or synthetic gibbsite, natural or synthetic doylite, natural orsynthetic nordstrandite, natural or synthetic bayerite andhydrargillite. Typically the particle size of the catalyst is in therange of 1 to 100 μm (e.g. 3, 5 or 10 μm) and its specific surface is inthe range of 75 to 250 m²/g (e.g. 100 or 150 m²/g).

[0017] The following table lists a representative number of compoundswhich are suitable in the first aspect of the present invention. TABLE ACrystalline aluminium oxides and hydroxides and characteristic linesaccording to Powder Diffraction File (PDF) d-values (in A) of theMaterial 3 strongest lines PDF # Alumina (Al-oxide) α-Al₂O₃ 2.07 2.521.59 48-366 β-Al₂O₃ 1.40 11.97 2.68 10-414 γ-Al₂O₃ 1.98 1.40 2.39 10-4251.40 2.41 2.12 13-373 1.40 1.98 2.39 29-63 δ-Al₂O₃ 1.39 2.60 2.4646-1215 Θ-Al₂O₃ 1.39 2.84 2.73 23-1009 Diaspore α-AlO(OH) 3.99 232 2.13 5-355 Boehmite, syn. y-AlO(OH) 6.32 1.85 3.16 49-133 Gibbsite, syn.Al(OH)₃ 4.85 4.37 2.39 33-18 Doylite Al(OH)₃ 4.79 437 2.39 38-376Nordstrandite, syn. Al(OH)₃ 4.79 2.27 4.32 24-6 Bayerite, syn. α-Al(OH)₃2.22 4.71 4.35 20-11 δ-Al(OH)₃ 3.62 2.27 1.80 37-1377 Hydrargillite (seegibbsite)

[0018] If not purely synthetic, these compounds frequently containsignificant amounts of Si, Fe, Na and/or other elements. β-Alumina,widely listed as such, is not a true aluminium oxide, but at least inpart a Na-aluminate. Many Al-compounds listed in Table A are alterationproducts, and are thus not highly crystalline. As indicated by thenames, most of these compounds are also known minerals. They areenvironmentally safe, which is an important aspect in the presentcontext.

[0019] Non-crystalline or X-ray-amorphous alumina can contain over 3% ofSi and is then mesoporous.

[0020] In all these compounds Al is octahedrally coordinated by oxygenwhereas in aluminosilicates (like felspars and zeolites) Al is intetrahedral coordination.

Preparation and testing of cigarettes containing alumina-based catalysts

[0021] For initial testing, the cigarettes were hand-rolled and thetobacco was loaded with 5% of the catalyst. This was done by using aprocedure wherein the tobacco is treated with catalytically activematerials, consisting of the steps of

[0022] a) distributing catalytically active material on tobacco,

[0023] b) pressing the catalytically active material on the tobacco.

[0024] Advantageously the catalytically active material is distributedevenly on the smoking tobacco. The tobacco can consist of leaves orreconstituted tobacco sheets, cut or uncut.

[0025] Advantageously the tobacco is made reasonably soft byconditioning it, i.e. it has a defined degree of moisture. If thetobacco is too dry it is brittle and not suitable for receiving thecatalytic material.

[0026] Preferably the catalyst is pressed on the tobacco by a single ordouble layer cylinder press. For a continuous working process such apress can work in combination with a conveyor belt. The process can becarried out with two or more distributing and pressing steps, e.g. onthe upper and lower side of the tobacco. E.g. the catalyst content inrelation to the tobacco is about 4-8% (wt/wt).

[0027] For PAH (polycyclic aromatic hydrocarbons) analyses, the methoddescribed by W. M. Meier and K.Siegmann [Microporous and MesoporousMaterials, 33 (1999) 307-310] was applied using a smoking machine. Thismethod is based on a photoelectric PAH sensor in combination with acommercially available light scattering instrument which determines thetotal mass of particles smaller than 10 μm (PM-10). The signal of thephotoelectric aerosol sensor is proportional to the amount of particlebound PAH. Light scattering reflects the number and size of particles,independently of chemical composition, and was found to agree with theresults obtained with conventional methods in numerous tests. The methodallows the simultaneous measurement of tar and PAH values.

Example 1

[0028] The tobacco blend (American blend type) was received from atobacco lot and kept in a humidifier at 60% relative humidity. 5% byweight of synthetic gibbsite (obtained from Fluka, Switzerland) wasevenly distributed over the tobacco, and then pressed on by a heavycylinder on a rubber belt.

[0029] Hand-rolled cigarettes of 1 g tobacco each were then preparedwithout filter tips, i.e. using tobacco with catalyst and withoutcatalyst (reference). The measurements gave reductions of

[0030] 48-53% PAH in the mainstream

[0031] 44-46% PAH in the sidestream

EXAMPLE 2

[0032] Following the same procedure as described in example 1, but usingα-alumina (supplied by Dr. Markus Meier, Sierre, Switzerland) and testedby X-ray diffraction. These gave the following results

[0033] in mainstream 49% reduction in PAH

[0034] in sidestream 45% reduction in PAH

Example 3

[0035] Following the same procedure as described in example 1, but usingX-ray amorphous Siral 1.5 (supplied by CONDEA GmbH, Hamburg, Germany)containing 1.5% silica and having a BET surface of 330 m2/g. Thefollowing results were obtained:

[0036] in mainstream 50-55% reduction in PAH

[0037] in sidestream 55-60% reduction in PAH

[0038] Note that the PAH reduction values in the mainstream are verymuch higher than those recorded for zeolite type catalysts (less than20% overall measured by the same method).

[0039] A smoking panel noted a smoother taste without off-taste in theproducts of the above examples.

1. Tobacco product carrying on its surface catalytically active materialfor improving the burning process, wherein the catalytically activematerial is selected from the group of crystalline and non-crystallineoxides and hydroxides of aluminium.
 2. Tobacco product according toclaim 1 wherein the catalytically active material is bound to thesurface, wherein the catalytically active material is preferably pressedinto the tobacco surface so as to be bound without an adhesive in orderto prevent the catalytically active material from being partially orcompletely inactivated by closed pores.
 3. Tobacco product according toclaim 1 or 2, wherein the oxides and hydroxides of aluminium are acid orslightly acidic.
 4. Tobacco product according to claim 1, wherein theoxides and hydroxides of aluminium contain Fe in an amount of less than3%.
 5. Tobacco product according to claim 1, wherein the catalyticallyactive material comprises crystalline hydroxides of aluminium whichcontain silicon in an amount of less than 3%.
 6. Tobacco productaccording to claim 1, wherein the catalytically active materialcomprises amorphous hydroxides of aluminium which contain silicon in anamount of more than 3%.
 7. Tobacco product according to claim 1, whereinthe catalytically active material is not highly crystalline.
 8. Tobaccoproduct according to claim 1, wherein the catalytically active materialcomprises particles consisting of single crystals.
 9. Tobacco productaccording to claim 1, wherein the catalytically active materialcomprises a granulate consisting of agglomerates of crystals which arebound to each other with a binder.
 10. Tobacco product according toclaim 9, wherein the binder is kaolinite.
 11. Tobacco product accordingto claim 1, wherein the catalytically active material comprises X-rayamorphous hydroxides of aluminium having a particle size in the range of1-100 μm and a specific surface of up to 550 m²/g.
 12. Tobacco productaccording to claim 1, wherein the catalytically active material isselected from the compounds of the group alumina (Al-oxide), diaspore,natural or synthetic boehmite, natural or synthetic gibbsite, natural orsynthetic doylite, natural or synthetic nordstrandite, natural orsynthetic bayerite and hydrargillite.
 13. Tobacco product according toclaim 1, wherein the particle size of the catalyst is in the range of1-100 μm, and its specific surface is in the range of 75 to 250 m²/g.14. A smokers' article comprising a filter, a tobacco rod and a wrapper,wherein the tobacco rod consists of a tobacco product according to claim1 or
 2. 15. Use of a catalytically active material comprising an oxideor hydroxide of aluminium for adding to the tobacco of a tobacco rod ofa smokers' article for reducing the amount of noxious compounds in themainstream and sidestream smoke in the combustion process of thesmokers' article during its consumption.
 16. Use according to claim 15,wherein the catalytically active material is selected from the groupconsisting of alumina, diaspore, natural or synthetic boehmite, naturalor synthetic gibbsite, natural or synthetic doylite, natural orsynthetic nordstrandite, natural or synthetic bayerite andhydrargillite.
 17. Use according to claim 16, wherein the catalyticallyactive materials comprise finely ground natural counterparts of oxidesand hydroxides of aluminium and granulated using a binder such askaolinite.